Follow
LIMITS OF DNA TESTING FOR FAMILY HISTORY
- 1. DNA alone cannot provide the name of an ancestor.
- 2. Percentage match of DNA alone cannot provide a definitive relationship.
- 3. Autosomal DNA cannot reliably reach back farther than five or six generations.
- 4. Y-DNA and mtDNA have strict inheritance patterns that limit their use.
- 5. There are significant limits on an 'ethnicity' or ancestry estimate that matches the DNA that you inherit.
1. DNA alone cannot provide the name of an ancestor.
DNA alone is not going to deliver your ancestors’ names to you, unless your close relative tests at the same company - but not your deceased ancestors: grandparents, great-grandparents, etc. For this you also need real genealogy records. Adapted from: Diahan Southard
2. Percentage match of DNA alone cannot provide a definitive relationship.
Even with the amount of DNA shared with biological parents and full siblings, there is always more than one possibility for how you’re related to someone you have a percentage match with (except an identical sibling). Because of recombination, full siblings generally share anywhere between 38–61% of their DNA (50% is only the average). The more distantly you’re related, the more possibilities for how you’re related.
Endogenous and bottleneck populations with a lot of intermarriage over generations can share significant amounts of DNA without having a recent common ancestor.
DNA gives us a genetic relationship range, or list of possible relationships, but we have to use other resources -historical records, trees, DNA analysis - to help us figure out which of the possible relationships is accurate (or at least most likely). Adapted from: Diahan Southard
3. Autosomal DNA cannot reliably reach back farther than five or six generations.
Fourth cousins tend to be genetically no more similar to each other than they are to any other individual from the same region.Beyond 5th cousins, these relationships can only be approached using triangulation of numbers of 'cousins', each with a documented family tree. There may be exceptions, but cases must be carefully documented. See Tested Haplogroups of People from History on GENI
4. Y-DNA and mtDNA have strict inheritance patterns that limit their use.
- Y-DNA shows only paternal lineage: it is inherited father to son and doesn’t mutate often, so it can help to determine which paternal line you originate from - but it can’t tell you exactly which person, as all males in that line carry that same Y-DNA.
- mtDNA testing looks exclusively at the lineage of your mother, her mother, and her mother, etc., where all females in that matriline pass on that mtDNA to their children, but only daughters pass it to theirs.
So, while mtDNA, for example, can trace a 100 x further back than atDNA, most (98%) of your relatives - such as your mother’s father’s mother’s people - are untouched by your Y-DNA and mtDNA tests.
Adapted from: Diahan Southard
5. There are significant limits on an 'ethnicity' or ancestry estimate that matches the DNA that you inherit.
The human genome has been decoded to a sufficient degree that modern testing companies can detect minute amounts of DNA that match DNA tested from living people from just about all ethnic regions. However those tiny amounts of detectable DNA cannot be used to identify your specific 'ethnicity' and much less who your ancestors were. No genetic variants have been found which are fixed within a continent or major region and found nowhere else. Ethnicity percentages are based on probability extrapolations of the ancestors of people tested in those regions, and a DNA company’s accuracy is only as good as its reference panels - indigenous people's DNA often being especially sparse. Two people from different regions can still have a genetic marker in common, and not everyone from a given region shares the exact same ones; they simply tend to have a significant number in common. “There is no Korean SNP or French SNP” - it's all probabilities: this particular SNP is a bit more common in France than it is in Korea. Human history is one of populations intermingling, so both nations and ethnicities are human inventions, their borders shifting over time. That's why, for example, when Ancestry.com released a 2020 update to its “ethnicity estimates”, a lot of people suddenly became more Scottish! There are a few exceptions to this rule, but they exist only for a very few WELL tested communities. Adapted from Caitlin Harrington and Human genetic variation